This is a proposal to begin a new research venture in studies of auditory cortex, in a laboratory that has previously been exclusively working in the cochlear nucleus. The aims of our exploration are threefold: (1) We will study synaptic function and connections between pairs of identified cortical neurons in auditory areas of the rat, using simultaneous intracellular recordings. (2) We will study long-term potentiation and depression of synaptic responses in the supragranular layers of primary and non-primary auditory cortex, with a particular focus on the timing relationship between synaptic activity and post-synaptic spiking, between pairs of identified cells. (3) We will examine changes in synaptic function from before the onset of hearing through early adulthood, to see whether synaptic plasticity is expressed differently during critical periods. These aims take advantage of our existing technical expertise and hardware, develop additional experimental capabilities, and begin the exploration of a new class of problems in auditory information processing.